Preparation of homopolymer and copolymers of (phosphonyl)aromatic diesters and acids

ABSTRACT

The composition of a homopolymer of (phosphonyl) aromatic diester compound using a catalyst and a glycol is provided. Further, the composition of a copolymer of the (phosphonyl) aromatic diester compound using a catalyst, a glycol and a second diester is provided. These polymers find application as flame retardants during synthesis of various polymeric materials.

FIELD OF INVENTION

The present invention is directed to polymers derived from(phosphonyl)aromatic diester and acid compounds and derivatives thereof.Polymers possessing (phosphonyl)aromatic diester and acids exhibit flameretadancy and can have utility as flame retardants in variousapplications.

BACKGROUND

Natural and synthetic polymers are being increasingly used under evermore demanding environmental conditions. Flame retardants are commonlyused to reduce combustibility of polymeric materials, such aspolycarbonates, polyesters and ployamides, has therefore become apivotal part of the development and application of new materials. (Chen,L., and Wang, Y-., Materials, 3: 4746-4760, 2010 and WO2010/132332A1).

Increasing flame retardancy of polymers has been addressed throughaddition of various flame retardants. For example organophosphoruscompounds have been used as flame retardants for polyesters, polyamidesand polycarbonates (WO2010/132332A1). Aryl polyphosphonates have beenused as flame retardants for polycarbonates and polyamides (Chen, L.,supra).

Polyesters such as polytrimethylene terephthalate (PTT), polyethyleneterephthalate (PET) and polybutylthylene terephthalate (PBT), find usein many application areas (such as carpets, home furnishings, automotiveparts and electronic parts) which require a certain level of flameretardancy. PTT provides desirable attributes such as stretch andrecovery, resiliency and stain resistance desirable in face fibers ofcarpets and is preferred to PET and PBT in such applications. In somecarpet construction of PTT fibers do not pass certain standardflammability tests without the use of flame retardant additives.

A number of flame retardants available to date contain various types ofhalogens (U.S. Pat. No. 4,131,594) which are not environmentallyacceptable. A need remains for new flame retardants, particularlynon-halogenated flame retardants, for use in polymers.

SUMMARY OF THE INVENTION

The current invention provides a composition of novel polymers of(phosphonyl)aromatic compounds with improved flame retardancy.

In one aspect, the present invention provides for a polymer comprisingrepeat units represented by structure IV

wherein

-   R₂(a) and R₂(b) are each independently H, C_(n)H_(2n+1), phenyl or    benzyl with the proviso that no more than one R_(2(a)) and no more    than one R_(2(b)) can be phenyl or benzyl;-   R₃(a) and R₃(b) are each independently C_(n)H_(2n+1), phenyl or    benzyl;-   R₄ is a C₁-C₆ alkylene radical;-   n is an integer of 1-10; and-   p is an integer of 1-10.

In another aspect, the present invention provides for a polymercomprising repeat units represented by structure IV and another repeatunits represented by the structure VI

wherein Q is a benzene radical or an ethylene radical or atetramethylene radical or a naphthalene radical or an octylene radical.

DETAILED DESCRIPTION

When a range of numerical values is provided herein, it is intended toencompass the end-points of the range unless specifically statedotherwise. Numerical values used herein have the precision of the numberof significant figures provided, following the standard protocol inchemistry for significant figures as outlined in ASTM E29-08 Section 6.For example, the number 40 encompasses a range from 35.0 to 44.9,whereas the number 40.0 encompasses a range from 39.50 to 40.49.

As used herein, the term “(phenoxy)aromatic” refers to the compound ofstructure (I). The term “halogenated (phosphonyl) compound” refers tothe compound of structure (II). The term “phenolic diester compound”refers to compound of structure (III).

In one aspect, the present invention provides a composition comprising a(phenoxy)aromatic compound represented by the structure (I)

wherein,

-   R₁(a) and R₁(b) are independently H, C_(n)H_(2n+1), phenyl or    benzyl;-   R₂(a) and R₂(b) are each independently H, C_(n)H_(2n+1), phenyl or    benzyl with the proviso that no more than one R₂(a) and no more than    one R₂(b) can be phenyl or benzyl;-   R₃(a) and R₃(b) are independently C_(n)H_(2n+1), phenyl or benzyl;-   n is an integer of 1-10; and,-   p is an integer of 1-10.

In an embodiment, R₁(a) and R₁(b) are the same.

In another embodiment, R₂(a) and R₂(b) are the same.

In yet another embodiment, R₃(a) and R₃(b) are the same.

In yet another embodiment R₁(a) and R₁(b) or H or C_(n)H_(2n+1) ormethyl.

In yet another embodiment R₁(a) and R₁(b) are H and R₃(a) and R₃(b) aremethyl.

In yet another embodiment R₃(a) and R₃(b) are methyl.

In yet another embodiment R₁(a), R₁(b), R₃(a) and R₃(b) are methyl.

In yet another embodiment R₂(a)and R₂(b) are C_(n)H_(2n+1) or H.

As can be noted in the structures above, the substituents can beattached to the aromatic ring at any point, thus making it possible tohave ortho-, meta- and para-substituents as defined above.

In one aspect, the present invention provides a process for preparingthe (phenoxy)aromatic compounds.

In one embodiment, the (phenoxy)aromatic compound is prepared bycontacting a halogenated (phosphonyl) compound of structure (II) whereinp, R₂(a), R₂(b), R₃(a) and R₃(b) are as defined above and x is O,

with a phenolic diester compound of structure (III) wherein R₁(a) andR₁(b) are as defined above,

one or more solvents and a base under reflux while stirring after whichthe reaction mixture is maintained under reflux for 48 hours until thedesired yield of reaction is achieved.

In one embodiment, the reaction is performed at a temperature in therange of 25-250° C. In a further embodiment the reaction is performed ata temperature in the range of 25-100° C. The reaction mixture is held atthe reaction temperature until the desired yield of reaction isachieved, and the reaction mixture is subsequently cooled.

The reaction of forming the (phenoxy)aromatic is catalyzed by one ormore base catalysts. Any catalyst that is capable of deprotonatingphenol can be used. That is, a suitable catalyst is any catalyst havinga pKa greater than that of phenol (9.95, using water at 25° C. asreference). Suitable catalysts include, but are not limited to, sodiummethoxide, calcium hydride, sodium metal, potassium methoxide, potassiumt-butoxide, potassium carbonate, benzyltrimethyl-ammonium hydroxide, andsodium carbonate. Preferred are potassium t-butoxide, potassiumcarbonate, sodium carbonate and benzyltrimethylammonium hydroxide.

The reaction for forming the (phenoxy)aromatic compound can beterminated at any desirable point by filtration to remove the catalyst,thereby terminating the reaction.

Suitable solvents useful for the current process include, but are notlimited to: aprotic solvents such as ethylacetate, toluene, xylenes,tetrahydrofuran and 1,4-dioxane

In the practice of the process for preparing the (phenoxy)aromaticcompound, a suitable halogenated phosphonyl compound and a suitablephenolic diester compound are contacted in the presence of one or moresuitable solvents and one or more suitable bases until the reaction hasachieved the desired degree of conversion. In one embodiment, thereaction is continued until no further product is produced over somepre-selected time scale. The required reaction time to achieve thedesired degree of conversion depends upon the reaction temperature, thechemical reactivity of the specific reaction mixture components, and thedegree of mixing applied to the reaction mixture, and can be readilydetermined by one skilled in the art. Progress of the reaction can bemonitored using any one of a variety of established analytical methods,including, but not limited to, nuclear magnetic resonance spectroscopy,thin layer chromatography, and gas chromatography. When the desiredlevel of conversion has been achieved, the reaction mixture is stopped,as described supra. In one embodiment, the stopped reaction mixture isconcentrated under vacuum, and rinsed with a solvent. Separation of theproduct thus produced can be effected by any method known to the skilledartisan such as, for example, distillation or column chromatography.

In one embodiment, the (phenoxy)aromatic diester compound formed can beconverted into a (phenoxy)aromatic diacid by contacting the(phenoxy)-aromatic diester compound with one or more base catalysts andan aqueous solution to provide a reaction mixture. The reaction mixtureis then stirred under reflux overnight. Following these steps, thereaction mixture is then cooled with concentrated hydrochloric acid andthe precipitate can be filtered off and dried under vacuum.

The (phosphonyl) aromatic diesters compounds disclosed herein can beused as additives in polymeric systems, such as polyesters, aramids, andnylons, to improve the flame retardancy of these polymers.

A homopolymer of the (phosphonyl) aromatic diesters compounds compriserepeat units represented by the structure IV

wherein

-   R₂(a) and R₂(b) are each independently H, C_(n)H_(2n+1), phenyl or    benzyl with the proviso that no more than one R_(2(a)) and no more    than one R_(2(b)) can be phenyl or benzyl;-   R₃(a) and R₃(b) are each independently C_(n)H_(2n+1), phenyl or    benzyl;-   R₄ is a C₁-C₆ alkylene radical;-   n is an integer of 1-10; and,-   p is an integer of 1-10.

In an embodiment, R₁(a) and R₁(b) are the same.

In another embodiment, R₂(a) and R₂(b) are the same.

In yet another embodiment, R₃(a) and R₃(b) are the same.

In yet another embodiment R₁(a) and R₁(b) or H or C_(n)H_(2n+1) ormethyl.

In yet another embodiment R₁(a) and R₁(b) are H and R₃(a) and R₃(b) aremethyl.

In yet another embodiment R₃(a) and R₃(b) are methyl.

In yet another embodiment R₁(a), R₁(b), R₃(a) and R₃(b) are methyl.

In yet another embodiment R₂(a)and R₂(b) are C_(n)H_(2n+1) or H.

In yet another embodiment R4 is propylene.

In one embodiment a homopolymer (structure V) of the (phosphonyl)aromatic diesters can be formed by reacting the diester compound with aglycol in the presence of a catalyst. The suitable catalyst for thisreaction can be titanium (IV) butoxide, titanium (IV) isopropoxide,antimony trioxide, antimony triglycolate, sodium acetate, manganeseacetate, and dibutyl tin oxide. The suitable glycol for this reactioncan be ethylene glycol, 1,3-propanediol, 1,4-butanediol, longeraliphatic diols, branched polyols, or branched diols.

In one embodiment for preparing the homopolymer, the (phosphonyl)aromatic diester is dimethyl5-((dimethylphosphoryl)methoxy)isophthalate, the catalyst is titanium(IV) isopropoxide and the glycol is 1,3-propanediol.

In another embodiment, the catalyst can be Titanium(IV)isopropoxide. Inyet another embodiment the alcohol can be 1,3-propanediol. The mixtureof the (phosphonyl) aromatic diester, the catalyst and the glycol can bestirred under nitrogen in the melt (solvent free) at a temperaturewithin the range of from room temperature (20-25° C.) to the refluxtemperature of the reaction mixture, preferably up to 180 to 240° C. for1-2 hours, to condensate methanol. Thereafter the mixture is furtherheated, preferably to a temperature within the range of 200 to 300° C.,and evacuated and stirred during 2-4 hours, to remove the excess alcoholand thereby form a polymer.

In another embodiment a copolymer (structure VII) comprising the repeatunits represented by the structure IV can be formed by reacting thecompound of structure IV with a glycol and a second diester/diacidcompound represented by the structure VI.

wherein

-   Q is a benzene radical or an ethylene radical or a tetramethylene    radical or a naphthalene radical or an octylene radical.    in the presence of a catalyst.

Suitable diesters or diacids include but not limited to dimethylterephthalate, terepthalic acid, 2,6-napthalene dicarboxylic acid,dimethyl 2,6-napthalenedicarboxylate, succinic acid, adipic acid, andsebacid acid. The suitable catalyst for this reaction can be titanium(IV) butoxide, titanium (IV) isopropoxide, antimony trioxide, antimonytriglycolate, sodium acetate, manganese acetate, and dibutyl tin oxide.The suitable glycol for this reaction can be ethylene glycol,1,3-propanediol, 1,4-butanediol, longer aliphatic diols, branchedpolyols, or branched diols. In another embodiment, the catalyst can beTitanium(IV)isopropoxide. Structure VII is shown below.

In one embodiment for preparing the copolymer dimethyl5-((dimethylphosphoryl)methoxy)-isophthalate can be reacted with1,3-propanediol, and dimethylterepthalate in the presence of Tyzor asthe catalyst.

EXAMPLES

The invention is further described but not limited by the followingspecific embodiments thereof.

Materials

The chemicals and reagents were used as received in the Examples asfollows:

Dimethyl-5-hydroxy isophthalate was obtained from Aldrich.

(Chloromethyl)dimethylphosphine oxide was obtained from VeZerfLaborsynthesen, GmbH, Germany.

(Chloromethyl)diphenylphosphine oxide, was prepared from(Hydroxymethyl)-dimethylphosphine oxide (obtained from VeZerfLaborsynthesen, GmbH, Germany) and thionyl chloride (obtained fromAldrich) as described by Qureshi, A. et al., (J. Chem. Res., 1998, 355).

The following chemicals were obtained from Sigma-Aldrich:titanium(IV)isopropoxide; dimethyl 5-hydroxyisophthalate and potassiumcarbonate.

The following chemicals were obtained from the DuPont Company,Wilmington, Del.: Bio based 1,3-propanediol (Bio-PDO™) and Sorona®Poly(trimethylene terephthalate) (PTT), bright 1.02 IV.

Methods Used to Measure Flame Retardancy

LOI (limited oxygen index) is a measure of the minimum oxygen contentneeded to sustain candle like burn. LOI can be determined from thermalgravimetric analysis (TGA) in air to limiting oxygen index (LOI)predictions using the following equation:

LOI=0.40×δ+17.5,

in which δ is char yield above 700° C.Char yield is the sample residue at given temperature that is notvolatilized during the heat treatment (Krevelen, Polymer,16: 615, 1975;and Li et al., Polym. Adv. Technol., 21: 229, 2010).

Molecular Weight by Size Exclusion Chromatography

A size exclusion chromatography system (Alliance 2695™ from WatersCorporation, Milford, Mass.), was provided with a Waters 414™differential refractive index detector, a multiangle light scatteringphotometer DAWN Heleos II (Wyatt Technologies, Santa Barbara, Calif.),and a ViscoStar™ differential capillary viscometer detector (Wyatt). Thesoftware for data acquisition and reduction was Astra® version 5.4 byWyatt. The columns used were two Shodex GPC HFIP-806M™ styrene-divinylbenzene columns with an exclusion limit of 2×10⁷ and 8,000/30 cmtheoretical plates; and one Shodex GPC HFIP-804M™ styrene-divinylbenzene column with an exclusion limit 2×10⁵ and 10,000/30 cmtheoretical plates.

For analysis, the samples were dissolved in1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) containing 0.01 M sodiumtrifluoroacetate by mixing at 50° C. with moderate agitation for fourhours followed by filtration through a 0.45 μm PTFE filter.Concentration of the solution was approximately 2 mg/mL.

Data was taken with the chromatograph set at 35° C., with a flow rate of0.5 ml/min. The injection volume was 100 microliters (μl). The run timewas 80 min. Data reduction was performed incorporating data from allthree detectors described above. 8 scattering angles were employed withthe light scattering detector. No standard for column calibration wasinvolved in the data processing

Thermal Analysis

Glass transition temperature (T_(g)) and melting point (T_(m)) weredetermined by differential scanning calorimetry (DSC) performedaccording to ASTM D3418-08. Thermogravic analysis (TGA) was performed ona TGA Q 500.from TA Instruments. Samples were heated to 800° C. at aramp rate of 10° C./min.

Example 1 Preparation of Dimethyl5-((Diphenylphosphoryl)methoxy)-isophthalate

In a dry box, dimethyl-5-hydroxy isophthalate (0.525 g, 0.0025 mol),(chloromethyl)diphenylphosphine oxide (0.625 g, 0.0025 mol), potassiumcarbonate (0.345 g, 0.00125 mol) and ethyl acetate (25.0 mL) were addedto an oven dried round bottom flask equipped with a reflux condenser anda stirring bar. The apparatus was removed from the dry box and undernitrogen, the contents were stirred for 48 hours under reflux. Theresulting material was cooled and filtered and the filtrate concentratedat reduced pressure. This concentrate was then purified using columnchromatography on a silica gel column with hexane/tetrahydrofuran (1:1by volume to 100% THF) and the eluants material was analyzed by thinlayer chromatography using having (hexane/THF (1:1 by volume) as asolvent. The compounds having an Rf of ˜0.22 were collected,concentrated at reduced pressure and dried under vacuum affording thedesired material, dimethyl 5-((diphenylphosphoryl)methoxy) isophthalate(0.30 g, 29.71% yield). The structure of the product was confirmed usingmass spectrometry and nuclear magnetic spectroscopy.

Example 2 Preparation of Dimethyl5-((Dimethylphosphoryl)methoxy)isophthalate

In a dry box, dimethyl-5-hydroxy isophthalate (1.05 g, 0.005 mol),(chloromethyl)dimethylphosphine oxide (0.315 g, 0.0025 mol), potassiumcarbonate (0.690 g, 0.005 mol) and ethyl acetate (50.0 mL) were added toa oven dried round bottom flask equipped with a reflux condenser and astirring bar. The apparatus was removed from the dry box and stirredunder nitrogen for ˜24 hours under reflux. The resulting cooled materialwas filtered and the filtrate concentrated at reduced pressure. Thisconcentrate was passed through a silica gel column using 5%methanol/tetrahydrofuran as the solvent. The collected fractions werecombined and concentrated at reduced pressure and dried under vacuumaffording the desired material, dimethyl5-((dimethylphosphoryl)methoxy)-isophthalate, (0.30 g, ˜40.0% yield).The structure of the product was confirmed using mass spectrometry andnuclear magnetic spectroscopy.

Example 3 Preparation of 5-((Dimethylphosphoryl)methoxy)isophthalic Acid

Dimethyl 5-((dimethylphosphoryl)methoxy)isophthalate (0.60 g g, 0.002mol), potassium hydroxide (1.11 g, 0.7 mol) and water (28.6 mL) wereadded to a round bottom flask equipped with a reflux condenser and astirring bar. The resulting mixture was stirred overnight under reflux.The cool reaction mixture was then made strongly acidic with conc. HCl.The precipitated acid was filtered off and dried under vacuum, affording0.40 g (69.32% yield) of the desired material,5-((dimethylphosphoryl)methoxy)isophthalic acid.

Example 4 Preparation of Dimethyl5-((Dimethylphosphoryl)methoxy)isophthalate

In a dry box, dimethyl-5-hydroxy isophthalate (21.00 g, 0.10 mol),(chloromethyl)dimethylphosphine oxide (6.3 g, 0.05 mol), potassiumcarbonate (13.8 g, 0.10 mol) and toluene (1.00 L) were added to a ovendried round bottom flask equipped with a reflux condenser and a stirringbar. The apparatus was removed from the dry box and under nitrogenrefluxed for ˜13 days. The resulting cooled material was filtered andthe filtrate concentrated at reduced pressure. This concentrate was thencolumn chromatographed with 5% methanol/tetrahydrofuran. The collectedfractions were combined and concentrated at reduced pressure and driedunder vacuum affording dimethyl5-((dimethylphosphoryl)methoxy)isophthalate (8.75 g, 58.30% yield). Thestructure of the product was confirmed using mass spectrometry andnuclear magnetic spectroscopy.

Example 5 Char Yield of Homopolymer from 1,3-Propanediol and Dimethyl5-((Dimethylphosphoryl)methoxy)-isophthalate

Dimethyl 5-((dimethylphosphoryl)methoxy)isophthalate was prepared asdescribed in Example 4.

Preparation of Copolymer of 1,3-Propanediol and Dimethyl5-((Dimethylphosphoryl)methoxy)-isophthalate

Dimethyl 5-((dimethylphosphoryl)methoxy)-isophthalate (72.9 g, 0.24mol), and 1,3-propanediol (33.3 g, 0.43 mol) were charged to a pre-dried250 mL three necked round bottom flask. An overhead stirrer and adistillation condenser were attached. The reactants were stirred at aspeed of 10 revolutions per minute (rpm) and the reaction mass was keptunder nitrogen_((g)) (N₂) purge atmosphere, the condenser was kept at23° C. The contents were degassed three times by evacuating down to 500mTorr and refilling back with N₂ gas.

Titanium(IV)isopropoxide catalyst (88 mg) was added after the firstevacuation. The flask was immersed into a preheated metal bath set at160° C. The solids were allowed to completely melt at 160° C. for 20minutes and the stirrer speed slowly increased to 180 rpm. Thetemperature was increased to 210° C. and maintained for 90 minutes todistill off most of the formed methanol. The nitrogen purge was closedand a vacuum ramp started, after about 60 minutes the vacuum reached avalue of 50-60 mTorr, and the reaction held for 3 hours. The over headstirrer was stopped and elevated from the floor of the reaction vesselbefore the vacuum was turned off and the system purged with N₂ gas. Theformed product was allowed to cool to ambient temperature and thereaction vessel was removed and the product recovered after carefullybreaking the glass with a hammer. Yield: ˜65 g (86%). M_(n) (SEC) ˜1400D, PDI ˜1.39. Char yield of copolymer of dimethyl5-((dimethylphosphoryl)methoxy)-isophthalate formed in (B) preparedabove was compared with Sorona® bright 1.02 IV (CE-A) and results areshown in Table 1 below.

TABLE 1 Comparison of char yield of copolymer formed in B with Sorona ®bright 1.02 IV (CE-A) Residual char at Estimated Sample 700° C. (%)¹LOI² copolymer of Dimethyl 5-((dimethyl- ~13 ~22.7phosphoryl)methoxy)-isophthalate CE-A Comparative example 1 which is 0~17.5 Sorona bright control, stated above. ¹From TGA analysis in air.²From equation: LOI = 0.40 × δ + 17.5* in which δ is char yield above700° C. As shown in Table 1, The char yield of copolymer of dimethyl 5((dimethylphosphoryl)methoxy)-isophthalate at 700° C. is ~13% indicatinga char forming ability of the polymer.

Example 6 Copolymer from 1,3-Propanediol, Dimethylterephthalate, andDimethyl 5-((Dimethylphosphoryl)methoxy)-isophthalate

Dimethyl 5-((dimethylphosphoryl)methoxy)isophthalate was prepared asdescribed in Example 4.

Preparation of Copolymer of 1,3-Propanediol, Dimethylterepthalate, andDimethyl 5-((dimethylphosphoryl)methoxy)-isophthalate

Dimethylterephtalate (DMT, 60 g, 0.309 mmol), dimethyl5-((dimethylphosphoryl)methoxy)-isophthalate (3 g, 0.01 mol, 5 wt % toDMT), and 1,3-propanediol (42.4 g, 0.55 mol) were charged to a pre-dried500 mL three necked round bottom flask. An overhead stirrer and adistillation condenser were attached. The reactants were stirred at aspeed of 50 rpm and the reaction mass was kept under nitrogen_((g)) (N₂)purge atmosphere, the condenser was kept at 23° C. The contents weredegassed three times by evacuating down to 100 Torr and refilling backwith N₂ gas. Titanium(IV)isopropoxide (20 mg) was added after the firstevacuation. The flask was immersed into a preheated metal bath set at160° C. The solids were allowed to completely melt at 160° C. for 20minutes after which the stirring speed was slowly increased to 180 rpm.The temperature was increased to 210° C. and maintained for 60 minutesto distill off the formed methanol. The temperature was increased to250° C. after which the nitrogen purge was closed and a vacuum rampstarted, after about 60 minutes the vacuum reached a value of 50-60mTorr. The reaction was held for 3 hours after which the polymerizationwas stopped by removing the heat source. The over head stirrer wasstopped and elevated from the floor of the reaction vessel before thevacuum was turned off and the system purged with N₂ gas. The formedproduct was allowed to cool to ambient temperature and the reactionvessel was removed and the product recovered after carefully breakingthe glass with a hammer. Yield ˜90% off white solid. The product wascharacterized by ¹H and ³¹P NMR providing the following details: ¹H-NMR(tce-d2) δ: 8.30 (s, ArH, 1H), 8.20-7.90 (m, ArH, 4H), 7.80 (s, ArH,2H), 7.65 (s, ArH, cyclic dimer), 4.65-4.40 (m, —CH ₂—COO—, 4H), 4.30(m, 2H, —O—CH ₂—P), 4.80 (m, 2H, —CH ₂—OH), 4.60 (m, DPG, 4H), 2.30-2.15(m, —CH₂—, 2H), 2.05 (m, DPG, 4H), 1.5 (m, 6H, —CH₃). ³¹P-NMR (tce-d2) δppm: 39. M_(n) (SEC) ˜22 400D, PDI ˜2.02. T_(m) (DSC) ˜226° C.,T_(g ˜)57° C.

What is claimed is:
 1. A polymer comprising repeat units represented bystructure IV

wherein R₂(a) and R₂(b) are each independently H, C_(n)H_(2n+1), phenylor benzyl with the proviso that no more than one R_(2(a)) and no morethan one R_(2(b)) can be phenyl or benzyl; R₃(a) and R₃(b) are eachindependently C_(n)H_(2n+1), phenyl or benzyl; R₄ is a C₁-C₆ alkyleneradical; n is an integer of 1-10; and, p is an integer of 1-10.
 2. Thepolymer of claim 1 wherein R₂(a) and R₂(b) are the same.
 3. The polymerof claim 1 wherein R₃(a) and R₃(b) are the same.
 4. The polymer of claim1 wherein R4 is propylene.
 5. The polymer of claim 1 further comprisingrepeat unit represented by the structure VI

wherein Q is a benzene radical or an ethylene radical or atetramethylene radical or a naphthalene radical or an octylene radical.6. The copolymer of claim 5 wherein the first repeat unit is dimethyl5-((dimehtylphosphoryl)-methoxy)-isophthalate and the second repeat unitis dimethyl terephthalate.